The present invention relates generally to manufacturing techniques for electronic components and more particularly to techniques for calibrating and adjusting operating characteristics of electronic components by programming non-volatile memory within the electronic components.
The process of manufacturing precision analog components, such as operational amplifiers, results in completed analog components with variable operating characteristics. This is generally due to normal variations in processes and materials used during manufacture.
Recently, in order to compensate for variations in the manufacture of analog components, manufacturers have provided fuses on the analog components. The fuses are connected to adjustable elements associated with analog devices on the analog component. The fuses may be selectively blown after manufacturing in order to adjust or xe2x80x9ctrimxe2x80x9d certain operating characteristics of the analog component. In this regard, aspects of a manufactured analog component""s operation may be measured and this measurement data may be used to determine which fuses to blow in order to trim the component so that it operates closer to predetermined specifications. Trimming is advantageous in many ways. For example, trimming allows manufacturers to offer analog components with greater accuracy and built in flexibility to optimize analog components for particular applications.
Conventionally, fuses on integrated circuit analog components have been implemented as segments of poly-silicon, metal or other material. These fuses are conventionally blown selectively, causing the fuse to create an open circuit, using a laser or by introducing a destructive electrical charge across the fuse through probe pads on the integrated circuit. Each of these techniques has several disadvantages.
First, blowing a fuse by laser or by destructive electrical charge applied to probe pads requires the fuses to be blown prior to packaging the integrated circuit. This is disadvantageous because the operating characteristics of the analog component, such as its offset voltage, may change as a result of the packaging process as well as the electrical characteristics of the package itself. Thus, trimming prior to packaging does not allow the manufacturer or anyone else to compensate for the effects of packaging on the analog component. Moreover, because most analog components are packaged prior to delivery to customers, it is generally not possible for customers to perform trimming.
Second, because blowing fuses in the conventional manner is destructive, it is not possible to undo the trimming process if desired. Additionally, blowing fuses may result in damaging passivation and other layers and structures on an integrated circuit. This damage may result in corrosion or other failure either immediately or over time.
Third, blown fuses may have conductive remnants which may migrate over time and reconnect leading to failure during operation in the field.
For the foregoing reasons, there is a need for a new technique for trimming analog components, and particularly those implemented as integrated circuits. There is a need to be able to perform the trimming either before or after packaging by the manufacturer, customer or third party if desired. There is a further need for trimming by a non-destructive process to avoid reliability problems and, in some instances, the irreversibility of destructive processes. There is still a further need for a trimming process which may be performed using a small number of input pins to the analog component.
According to the present invention, trimming of an operational amplifier is performed electrically using non-volatile fuses. The non-volatile fuses may be programmed electrically without destroying any passivation layers or other devices on the electronic component. In the case of an integrated circuit analog component, the trimming may be performed either at the wafer level or at the packaging level. Trimming at the packaging level permits the trimming to be performed to compensate for packaging induced variations. It also allows trimming to be performed by customers or other third parties on the packaged parts. Moreover, when implemented as erasable non-volatile fuses, the fuses may be programmed more than once. The trimming may be performed specifically to adjust the quiescent current or offset voltage of an operational amplifier.
According to one embodiment of the invention, an operational amplifier includes a pair of input pins and an output pin, analog devices and non-volatile fuses. The analog devices are coupled to the pair of input pins and the output pin. The analog devices are operative to amplify differences in signals on the pair of inputs and output an amplified difference signal. The analog devices include adjustable elements for adjusting an offset voltage of the operational amplifier. The non-volatile fuses are coupled to the adjustable processing elements and are electrically programmable to adjust the adjustable processing elements to alter the offset voltage.
The operational amplifier is typically implemented as an integrated circuit. The adjustable elements within the operational amplifier may include switches, each being connected in series with a load device. The non-volatile fuses may be controllably coupled to the switches to activate one or more of the load devices and to change the offset voltage. The operational amplifier may further include registers for storing fuse configuration data received from a data pin. A multiplexer may be coupled between outputs of the registers and outputs of the nonvolatile fuses, and inputs to the adjustable elements. The multiplexer is operable to provide configuration data from the registers to the adjustable elements during a calibration mode and from the non-volatile fuses to the adjustable elements after programming of the analog component.
A method of programming an operational amplifier according to an embodiment of the invention includes loading calibration data into the operational amplifier and measuring output signals from the operational amplifier when configured with the calibration data. The loading and measuring are repeated with different values for the calibration data until desired calibration data is determined. The non-volatile fuses are electrically programmed on the operational amplifier with the desired calibration data.
The method may further include verifying the proper programming of the non-volatile fuses and programming the non-volatile fuses with a fuse lock value at the end of the programming. The method may be used, for example, to trim the quiescent current or offset voltage of the operational amplifier.
In another embodiment of the invention, an operational amplifier, includes a pair of input pins and an output pin, analog devices and non-volatile fuses. The analog devices are operative to amplify differences in signals on the pair of inputs and output an amplified difference signal. The analog devices include adjustable elements for adjusting a quiescent current of the operational amplifier. The non-volatile fuses are coupled to the adjustable processing elements. The non-volatile fuses are electrically programmable to adjust the adjustable elements to alter the quiescent current. The adjustable elements may include a resistor stack and switches. The resistor stack is biased by a current derived from the quiescent current and has a plurality of tap points. Each switch is coupled at one end to a respective one of the tap points and is coupled at the other end to each other switch. The non-volatile fuses are controllably coupled to the switches to select one of the tap points. The other end of the switch is coupled to a bias amplifier which changes the quiescent current based on the selected tap point.